1. Field of the Invention
The present invention relates to a method of manufacturing an assembly of an optical waveguide substrate comprising a main body and at least one optical waveguide formed in or on the main body and at least one optical fiber aligning substrate including a main body and at least one optical fiber held on the main body.
2. Description of the Related Art Statement
Recently there has been proposed a technique for forming an optical waveguide substrate by inwardly diffusing titanium into a main body made of a monocrystal of lithium niobate (LiNbO.sub.3). Such an optical waveguide substrate may be utilized as a substrate for a waveguide type light modulator, a waveguide type branch and couple circuit and a waveguide type multiplexer and demultiplexer circuit. In the above mentioned optical waveguide substrate, it is necessary to couple an end face of an optical fiber with an end face of the light waveguide so that the light can be transmitted there-through at a high efficiency. That is to say, when there is formed a space between these end faces of these elements or the optical axes of these end faces are not aligned with each other, there might be produced a large loss in the light transmission, and thus these end faces have to be coupled with each other at a high precision.
There have been proposed various methods of coupling the end faces of these optical elements. In almost all methods, a laser light beam is actually transmitted between these optical elements and the adjustment is performed such that an amount of transmitted laser light becomes maximum. However, this requires a very long time and the working efficiency is low, so that the production efficiency becomes also low.
In Japanese Patent Application Laid-open Publication Kokai Hei 2-125209, there is disclosed a known method which could mitigate the above explained drawbacks. In this known method, guide grooves are formed in one surface of the optical waveguide substrate and guide pins are provided on a connector for supporting the optical fibers, and when the optical fiber aligning substrate is coupled with the optical waveguide substrate, the guide pins are inserted into the guide grooves. Then, the end face of the optical waveguide substrate is automatically aligned with the end face of the optical fiber aligning substrate.
In the above explained known method, upper and lower plates of the optical fiber holding connector are formed by silicon chips or plastic plates, so that it is very difficult to couple the end faces of the optical waveguides and the end faces of the optical fibers with each other precisely, and thus it is very difficult to obtain a high light coupling efficiency.
The inventors have tried to form the optical waveguides in the substrate and the optical fibers are inserted into V-shaped grooves formed in a surface of the optical fiber aligning substrate, and after end faces of these substrates have been precisely processed mechanically and polished optically, they are coupled with each other, while contours of the substrates are used as reference surfaces. However, this process has a limitation in the coupling precision between the end faces of the optical waveguide substrate and those of the optical fiber aligning substrate, and therefore a cumbersome adjustment of the optical axes is still required.